heres how i did it and never had an issue with a full automatic 904. put the gear selector in 2nd gear.. start the burnout and allow it to go into 2nd gear (it will do it on its own) then bump it into 3rd gear and come out of the water in 3rd gear.
Thanks, that finally answers my two concerns: a) explain in detail, first-hand, how someone with a full auto valve body is doing their burnout and b) how to avoid damage to the transmission while doing so.
And regarding the manual valve body option, perhaps other members of the family driving my car may not want to shift manually. Personally, I don't have a preference.